Along with recent rapid development of light-weight low-cost projection apparatuses, development of image synthesization units (image synthesizing means) is underway, since image synthesization units are important parts of such projection apparatuses.
For example, Chinese Utility Model No. 200620133278.7 discloses an image synthesization unit 3 coupled to an optical system 2 of a projection apparatus as shown in FIGS. 8 and 9.
In this utility model, white light emitted from a lamp unit 4 is led to a first dichroic mirror 26 via a first integrator lens 21, pre-stage light-shielding lattice 23, second integrator lens 22, post-stage light-shielding lattice 24, polarization prism plate 25, and condenser lens 20.
The first integrator lens 21 and the second integrator lens 22 each consist of fly-eye lenses made of a heat-resistant glass to make uniform the illuminance distribution of the white light emitted from the lamp unit 4.
The pre-stage and post-stage light-shielding lattices 23 and 24, respectively, are made of a thin aluminum plate. They are provided to shield unwanted light that would be otherwise incident on the polarization prism plate 25.
The light, which has passed through the polarization prism plate 25, reaches the first dichroic mirror 26 through a condenser lens 20.
The first dichroic mirror 26 reflects only blue light and transmits red and green lights, while the second dichroic mirror 27 reflects green light and transmits red light. A field mirror 28 reflects red light.
Thus, the white light emitted from the lamp unit 4 is decomposed into green, blue, and red lights by means of the first and second dichroic mirrors 26 and 27, respectively, before the light is led to the image synthesization unit 3.
As shown in FIGS. 9 and 10, the image synthesization unit 3 has: a cubic color synthesization prism 31; a prism pedestal 30 consisting of an upper and lower prism pedestals 301 and 302, respectively, for fixing therebetween the color synthesization prism 31; liquid crystal panels 33b, 33g, and 33r, respectively, for blue, green, and red light (referred to as blue, green, and red liquid crystal panels, respectively) arranged on three different sides of the color synthesization prism 31; and liquid crystal panel holders 38b, 38g, and 38r for fixing thereon corresponding liquid crystal panels 33b, 33g, and 33r. The liquid crystal panel holders 38b, 38g, and 38r are jointed together by the prism pedestal 30 to form the integral image synthesization unit 3.
The blue light reflected by the first dichroic mirror 26 and by the field mirror 29a shown in FIG. 8 is led to a condenser lens 35b, and, after passing through it, reaches the color synthesization prism 31 via a polarization plate for blue incident light (referred to as blue polarization plate) 32b, liquid crystal panel for blue light (referred to as blue liquid crystal panel) 33b, and polarization plate for emerging blue light (referred to as emergence blue polarization plate) 34b. 
The green light reflected by the second dichroic mirror 27 is led to the condenser lens 35g, and, after passing through it, reaches the color synthesization prism 31 via a polarization plate for green incident light (referred to as green incident polarization plate) 32g, liquid crystal panel for green light (referred to as green liquid crystal panel) 33g, and polarization plate for emerging green light (referred to as emergence green polarization plate) 34g. 
The red light reflected by the field mirrors 28 and 29b are led to a condenser lens 35r, and, after passing through it, reaches a polarization plate for red incident light (referred to as red incident polarization plate) 32r, liquid crystal panel for red light (referred to as red liquid crystal panel) 33r, and polarization plate for emerging red light (referred to as emergence red polarization plate) 34r. 
The imaging lights of three primary colors led to the color synthesization prism 31 are synthesized by the color synthesization prism 31 into a single beam of colored imaging light, which is projected onto a front screen through a projection lens 39.
Referring to FIGS. 9 and 10 again, the color synthesization prism 31 is securely fixed in position by the upper and lower prism pedestals 301 and 302, respectively. The liquid crystal panel holders 38b, 38g, and 38r are fixed to the upper and lower prism pedestals 301 and 302, respectively.
The blue, green, and red liquid crystal panels 33b, 33g, and 33r are respectively fixed to three mounting members 37 with screws.
The three mounting members 37 are respectively soldered to the liquid crystal panel holders 38b, 38g, and 38r after they are optically aligned for correct collimation and focusing of imaging lights.
The liquid crystal panel holders 38b, 38g, and 38r are in turn fixed to the prism pedestal 30 by means of multiple screws 3801 that penetrate holes (not shown) of the liquid crystal panel holders 38b, 38g, and 38r and are screwed into threaded bores (not shown) formed in the prism pedestal 30. However, such fixation of the liquid crystal panel holders 38b, 38g, and 38r to the prism pedestal 30 is not satisfactory for the following reasons.
First, each of the liquid crystal panel holders 38b, 38g, and 38r need be simultaneously assembled onto at least two sides (referred to as assembling faces) of the upper and lower prism pedestals 301 and 302, which will result in precision errors of the liquid crystal panel holders, which in turn causes deformations of the liquid crystal panel holders during their assembly, which deformations affects collimation of light by the optical system.
As shown in FIG. 10, the respective liquid crystal panel holders 38b, 38g, and 38r have soldering joint sections 380 located at a significant distance from the respective screws 3801. As a consequence, the soldering joint sections 380 are likely to undergo significantly large deformations around the screws 3801 serving as fixed supports of the soldering joint sections 380. Such large deformations of the soldering joint sections directly affect the collimation of light.
Further, the three liquid crystal panel holders 38b, 38g, and 38r fixed on the three sides of the prism pedestal 30 add weight and cost to the image synthesization unit 3.
Therefore, there is a need for a liquid crystal projection apparatus equipped with an image synthesization unit that is free of such drawbacks as mentioned above.